1. Technical Field
The present invention relates to a method of manufacturing a solar battery.
2. Related Art
A solar battery is known which uses polycrystalline, microcrystalline, or amorphous silicon. In particular, a solar battery having a structure in which microcrystalline or amorphous silicon thin films are layered has attracted much attention in view of resource consumption, cost reduction, and improved efficiency.
In general, a thin film solar battery is formed by sequentially layering a front side electrode, one or more semiconductor thin film photoelectric conversion units, and a back side electrode over a substrate having an insulating surface. Each solar battery unit is formed by layering a p-type layer, an i-type layer, and an n-type layer from a side of incident light. In addition, a technique is employed in which the back side electrode is formed in a layered structure of a transparent conductive film and a metal film so that the incident light is reflected and the photoelectric conversion efficiency in the semiconductor thin film photoelectric conversion unit is improved.
For example, Japanese Patent No. 3419108 discloses a method of layering a back side electrode layer comprising a transparent conductive metal compound layer and a metal layer over a semiconductor thin film photoelectric conversion unit by moving a substrate in plasma regions where the transparent conductive metal compound and the metal are provided adjacent to each other, from the side of the transparent conductive metal compound to the side of the metal.
When the layered structure of the transparent conductive film and the metal film is employed as the back side electrode, the metal film is formed over the transparent electrode film. In this process, if a wait time from completion of formation of the transparent electrode film to the start of the formation of the metal film is elongated, the charges charged on the substrate during the time when the substrate is exposed to the plasma for sputtering the transparent electrode film may be discharged, and the film quality of the transparent conductive film and the metal film may be degraded because of the relationship between the plasma potential and the substrate potential when the substrate is exposed to the plasma for sputtering the metal film.
In addition, if the wait time after the substrate has passed the plasma for sputtering the transparent electrode film and until the substrate reaches the plasma for sputtering the metal film is elongated, it is not possible to take advantage of the heating of the substrate by plasma of the sputtering during the formation of the transparent electrode film, and the temperature of the substrate is reduced before the formation of the metal film.
In particular, in an inline-type manufacturing device in which the substrate is moved and passed through a plasma for sputtering the transparent electrode film and further through a plasma for sputtering the metal film, an in-plane distribution of the substrate temperature would be caused in one substrate between a region which passes through the plasma of the transparent electrode film earlier and a region which passes through the plasma later. Such an in-plane distribution affects the characteristics of the formed transparent electrode film and the formed metal film, and may increase non-uniformity on the surface of the film or may reduce the film quality.